The present invention relates to magnetically actuated reed switch assemblies, and particularly to such a reed switch assembly having a desired level of sensitivity to the magnetic field of an actuating magnet and an improved method for manufacture of such a switch assembly.
Holce U.S. Pat. Nos. 4,210,888 and 4,213,110 disclose "wide gap" magnetic reed switch assemblies, in which a magnetic reed switch is accompanied by a helper magnet which provides a portion but not all of the magnetic flux density required to actuate the magnetic reed switch. The amount of magnetic flux density provided by the helper magnet is too small to keep the magnetic reed switch in a magnetically actuated state, but allows an actuating magnet to operate the switch at a greater distance than otherwise would be possible. Holce further discloses the adjustment of the sensitivity of the switch assembly to provide actuation when an actuating magnet is separated from the reed switch assembly by a desired distance, by adjusting the position of the helper magnet longitudinally of the reeds of the reed switch.
The manufacture of the reed switch assemblies disclosed in each of the Holce patents just mentioned requires some adjustment of the position of the helper magnet relative to the reed switch, in order for the switch assembly to perform its function in the most desired manner. That is, some adjustment of the helper magnet position is necessary to provide that the reed switch will become magnetically actuated when a properly polarized and oriented permanent actuating magnet of the proper size is located at a desired distance from the reed switch assembly. Such adjustment of the position of the helper magnet is also important in order to ensure that the reed switch not latch. That is, the magnetic reeds should separate and again become unactuated when the actuating magnet is withdrawn to a distance from the magnetic reed switch assembly.
Magnetic reed switches are particularly well adapted for use in burglar alarm sensing circuits and other proximity sensing applications, since their encapsulated structure and small size make it possible to mount such switches unobtrusively, and because a switch assembly including such a magnetic reed switch can be made to be sensitive to the magnetic field of a relatively small permanent magnet carried on a movable object such as a door, gate, or window whose unauthorized movement is to be detected by the alarm system, or on a moving element of a machine whose operation is to be controlled by a circuit including the reed switch.
Magnetic actuation of a magnetic reed switch requires a magnetic flux density which an actuating magnet acting alone can provide only when the actuating magnet is relatively close to the switch assembly. When a helper magnet is located very close to the reed switch it can provide a portion of the magnetic flux density required for magnetic actuation of the reed switch and thus allow a wider gap between the switch and an actuating magnet. In some applications it is highly desirable to have a magnetic reed switch remain magnetically actuated, despite inconsequential amounts of movement of a gate, door, or other moving member carrying the actuating magnet for the switch, in order, e.g., to avoid false alarms resulting from normal movement caused by wind or other causes short of an unauthorized entry, where the magnetic reed switch is part of a burglar alarm system.
It is also desired to be able to actuate a magnetic reed switch and maintain it in a magnetically actuated state without the need for particularly large actuating magnets. While these performance objectives are attained in switches manufactured in accordance with the Holce patents mentioned, proper adjustment of the position of the helper magnet during manufacture of such switches takes time and requires trained workers.
It is therefore desired to provide a magnetic reed switch assembly having capabilities equivalent to those achieved by the devices of Holce U.S. Pat. Nos. 4,210,888 and 4,213,110, with respect to the distance at which an actuating magnet may be separated from the switch assembly, and to manufacture such a switch assembly at a cost which is less than that of previously known magnetic reed switch assemblies including helper magnets.